Structure to interconnect two branches of a suspension bridge framework in correspondence of a pier supporting the catenary

ABSTRACT

A suspension bridge having end piers from which the bridge is suspended. The bridge has a substantially fixed stiff horizontal branch (P1) and a substantially flexible horizontal branch (P2). Each bridge branch (P1, P2) comprises three parallel longitudinally extending mutually spaced box-like bodies comprising a central body (S1) and two lateral bodies (S2, S3). Transverse ledgers (T) are located at regular intervals along the bridge and interconnect the three bodies. There is a gap between the two bridge branches (P1, P2) and in the gap there is a central body section (S1&#39;) fixedly interconnecting the central longitudinal bodies (S1) of the two bridge branches (P1, P2). Also in the gap there are two lateral body sections (S&#34;) extending between and slidable relative to the lateral bodies (S2, S3) of the two bridge branches (P1, P2). A vertical hinge joint, also in the gap, interconnects the bridge branches (P1, P2) and lies on the central longitudinal axis of the bridge.

FIELD OF THE INVENTION

The present invention concerns suspension bridges comprising anessentially flat main structure, or framework, the top surface of whichforms the roadway for the transport means crossing the bridge, and asuspension system formed of catenary cables anchored to end piers of thebridge and of a plurality of vertical stays or hangers to suspend thebridge framework to the catenary cables.

BACKGROUND OF THE INVENTION

As known, these suspension bridges are highly exposed to winds, theeffects of which have to be taken into account--in many respects--whenplanning the bridge. The present invention particularly concerns theeffects produced by crosswind pressure, which tends to cause ahorizontal inflection of the bridge framework, thereby creatingremarkable stresses especially in correspondence of the point ofanchorage of said framework to the end piers supporting the bridge.

It is also known, in fact, that this area of the bridge framework issubject to stresses, which become higher--on the one hand--the wider thespan of the bridge, and--on the other hand--the longer the distance ofthe bridge lateral edges from its central axis.

In a bridge--for instance like that described in EP-A-0,233,528, filedby the same Applicant--having a span wider than 3 Km and a transversalverse dimension of about 50 m, the stresses in correspondence of thepoint of anchorage of the framework to the end piers can becomeinadmissible.

Hereinafter, reference is made to a bridge framework formed of a fixedstiff branch--corresponding to the framework part extending from thepier axis towards the embankment--and of a flexible branch,corresponding to the framework part extending from the pier axis towardsthe central bay. Of course, this assumption is quite arbitrary since, inreal fact, no part of the bridge framework can be considered totallyfixed and stiff; nevertheless, it helps to better understand theinvention and define its contents in a conventional way.

OBJECT OF THE INVENTION

The object of the present invention is to thus propose a structure tointerconnect two branches--a substantially fixed stiff branch and asubstantially flexible branch--of a suspension bridge framework, incorrespondence of the end piers supporting the bridge, said structureallowing to substantially reduce the stresses determined by horizontalinflection.

SUMMARY OF THE INVENTION

This result is obtained--in a bridge framework, wherein each of saidbranches comprises three parallel longitudinal, mutually spaced,box-like bodies, a central body for railway traffic and two lateralbodies for roadway traffic, said bodies being interconnected bytransverse ledgers positioned at regular intervals along the bridge--dueto the fact that said structure comprises: a central body sectionforming a fixed joint between the central longitudinal bodies of the twobridge branches; two lateral body sections mounted slidable in respectof the lateral longitudinal bodies of the two bridge branches; and ahinge joint between said bridge branches, in correspondence of the pieraxis.

The invention is based on the consideration that, when a bridge isoverstressed by horizontal inflection, it is possible to annul theover-stressing effects by interrupting the solution of continuity incorrespondence of the end piers supporting the bridge, and providing fora hinge system--instead of a fixed joint--to prevent the horizontalinflection of the bridge from being transmitted to the end piers.

On the other hand, to allow railway traffic to take place in safeconditions, it is necessary to preserve the continuity of the horizontalrotation of the bridge at least in correspondence of the railway trafficlane.

These contrasting requirements are now in fact brilliantly solved by thepresent invention, according to which the continuity is preserved forthe central longitudinal body of the bridge--designed for railwaytraffic and, besides, also less subject to stresses--while a hingesystem is provided for the lateral sections of the bridge, designed forroadway traffic.

BRIEF DESCRIPTION

Further characteristics and advantages of the interconnecting structureaccording to the present invention will anyhow be more evident from thefollowing detailed description of a preferred embodiment thereof, givenby way of example and illustrated on the accompanying drawings, inwhich:

FIG. 1 is a diagrammatic plan view of the suspension bridge framework,work, in correspondence of its point of anchorage to an end pier; and

FIG. 2 is a section view along the line II--II of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

As shown on the drawings, the bridge framework is formed of threeparallel longitudinal, mutually spaced, box-like bodies--a central bodyS1 and two lateral bodies S2 and S3--interconnected by transverseledgers T positioned at regular intervals along the bridge, as describedmore in detail in another patent application being simultaneously filedby the same Applicant.

It is evident from FIG. 1 that, in correspondence of the end piers--eachcomprising two pillars M1 and M2--the fixed stiff branch P1 of thebridge terminates with the ledger T1, while the flexible branch P2 ofthe bridge terminates with the ledger T2. Between these ledgers T1 andT2 there is a central section of the bridge framework which forms theinterconnecting structure between the two branches P1 and P2.

Said ledgers T1 and T2 form first of all the base of two triangles, theoblique sides of which are formed by a pair of beams A1 and,respectively, A2; these latter converge at the centre on the verticalaxis of the pier, which is also the hingeing axis of said two triangles.

On said hingeing axis there is provided a hinge pin C, onto which isarticulated a transverse rod D, the other end of which is articulated tothe side of the pillar M1 (see also FIG. 2), preferably by way of a balljoint.

In the area of the interconnecting structure above said twotriangles--and according to the fundamental characteristic of thepresent invention--there are positioned:

a central box-like body S1', which forms a continuation of both centrallongitudinal bodies S1 of the flexible branch P2 and, respectively, ofthe fixed stiff branch P1 of the bridge; this body S1' also forms whatis defined as a fixed joint between said two bodies S1; as can be seenfrom FIG. 2, the hinge pin C is carried by an anchor base C1 projectingfrom the bottom of the body S1';

two lateral box-like bodies S", which are mounted slidable in respect ofthe lateral longitudinal bodies S2 and S3 of the branches P1 and P2 ofthe bridge; this slidable assembly of the bodies S", together with thehinge assembly of the ledgers T1 and T2 on the pin C, form what isdefined as a hinge joint between the branches P1 and P2 of the bridge.

As can be easily seen from the drawings, the fixed joint and thedescribed hinge joint can be considered to coincide with the verticalaxis of the pier. Hence, the ledger T2 of the flexible branch P2 of thebridge can "rotate" sideways even considerably, under crosswindpressure, without causing any stresses on the lateral bodies S2 and S3of the bridge (roadway traffic lanes), while the inflection undergone bythe central body S1-S1' (railway traffic) has very limited effects,since this section is positioned close to the central symmetry axis ofthe bridge where there are no stresses.

This fixed and hinge joint system is completed by the spacing rod D,which--as already said--is meant to prevent impact between the pier andthe bridge framework, for instance due to oscillations or movementscaused by wind pressures or seismic actions. Thanks to its articulationat both ends, the rod D produces no strains on the structure.

It is to be understood that the invention is not limited to theparticular embodiment described heretofore, which only forms a veryschematic and non-limiting example thereof, but that several embodimentsare possible, all within reach of an expert of the art, without therebydeparting from the scope of the invention itself.

I claim:
 1. A suspension bridge having end piers from which a bridge issuspended, the bridge comprising a substantially fixed stiff horizontalbranch (P1) and a substantially flexible horizontal branch (P2), eachbridge branch (P1, P2) comprising three horizontal parallellongitudinally extending mutually spaced box-like bodies comprising acentral body (S1) and two lateral bodies (S2, S3), transverse ledgers(T) located at regular intervals along the bridge and interconnectingsaid bodies, there being a gap between the two bridge branches (P1, P2)and in the gap there being a central body section (S1') fixedlyinterconnecting the central longitudinal bodies (S1) of the two bridgebranches (P1, P2); also in the gap there being two lateral body sections(S") extending between and slidable relative to said lateral bodies (S2,S3) of the two bridge branches (P1, P2); and in the gap a vertical hingejoint interconnecting said bridge branches (P1, P2) and lying on acentral longitudinal axis of the bridge.
 2. A bridge as claimed in claim1, each of said three longitudinal box-like bodies (S1, S2, S3)comprising a traffic lane of the bridge, said central bodies (S1) ofboth of said branches and said central body section (S1') comprising acontinuous stiff structure extending along the two branches (P1, P2) ofthe bridge.
 3. A bridge as claimed in claim 2, wherein said continuousstiff structure (S1, S1') supports a railway traffic lane.
 4. A bridgeas claimed in claim 1, wherein said central body section (S1') carriesat its center a downwardly projecting anchor base (C1) to which isconnected a pin (C) comprising a part of said hinge joint and definingsaid axis.
 5. A bridge as claimed in claim 1, and a pair of beams (A1,A2) secured at one end to spaced points along each of two said ledgers(T1, T2), one of said two ledgers (T1) being secured to said stiffbranch (P1) and the other of said two ledgers (T2) being secured to saidflexible branch (P2), said beams converging on and being secured to saidhinge joint.
 6. A bridge as claimed in claim 5, further comprising atransverse spacing rod (D) articulated at one end to a said pier and atanother end to said hinge joint.